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Numerical Simulation Model (numerical + simulation_model)
Selected AbstractsA Numerical Simulation Model for Shield Tunnelling with Compressed Air SupportGEOMECHANICS AND TUNNELLING, Issue 3 2008Felix Nagel Dipl.-Ing. This paper is concerned with a numerical simulation model (ekate) specifically designed for shield tunnelling in fully and partially saturated soils based upon the Finite Element Method (FEM). The model considers all relevant components , the soil, the lining, the tail void grouting, the hydraulic jacks and different types of face support , involved in shield tunnelling. The surrounding soft soil is formulated as a three-phase material, consisting of the soil skeleton, pore water and air. This model allows for the simulation of consolidation processes in partially saturated soils as well as of flow of compressed air often used as temporary face support during repair interventions at the cutting wheel. Despite the complexity connected with the relatively high degree of realism of the simulation model, only little effort is required from the user to establish a realistic 3D model for shield tunnelling. To this end an automatic model generator has been developed which allows for a user friendly generation of the discretized model including all components involved and to investigate variants with a minimum effort for the user. The model allows for realistic predictions of settlements and also provides information on deformations and stresses in the ground, the lining and the TBM, respectively. In addition to its use as a prognosis tool in the design process, in particular for tunnelling projects in sensitive urban areas, the model also may be used to assist the driving and steering process in mechanized tunnelling. The paper provides an overview over the main components of the model, the automatic model generator and the tri-phasic representation of the soil. A simulation of a compressed air intervention of a shield tunnel in soft soil demonstrates the applicability of the model. Ein numerisches Simulationsmodell für druckluftgestützte Schildvortriebe In diesem Beitrag wird ein Simulationsmodell basierend auf der Methode der Finiten Elemente (FEM) für die Berechnung schildvorgetriebener Tunnel in un-, voll- und teilgesättigten Böden vorgestellt. In diesem numerischen Modell werden alle beim maschinellen Tunnelbau wesentlichen Komponenten , der Boden, der Ausbau, die Schildschwanzverpressung, die Vortriebspressen sowie unterschiedliche Arten der Ortsbruststützung , wirklichkeitsnah berücksichtigt. Der Baugrund wird im Simulationsmodell als dreiphasiges Material modelliert, bestehend aus dem Korngerüst, dem Porenwasser und der Porenluft. Diese Materialformulierung für den Baugrund ermöglicht die Analyse von Konsolidierungsprozessen in teilgesättigten Böden ebenso wie von Strömungsvorgängen im Boden bei Verwendung von Druckluft als temporärer Ortsbruststützung. Druckluft wird häufig beim Wechsel von Schneidwerkzeugen eingesetzt. Ungeachtet der Komplexität des Modells, die mit der relativ wirklichkeitsnahen Abbildung des Vortriebsgeschehens verbunden ist, ist nur ein sehr geringer Aufwand für die Modellgenerierung erforderlich. Um diesen Eingabeaufwand auf ein Minimum zu reduzieren, wurde ein automatischer Modellgenerator entwickelt, der den Ingenieur bei der Eingabe unterstützt und die Untersuchung von Planungsalternativen deutlich vereinfacht. Das Modell ermöglicht wirklichkeitsnahe Prognosen von Bodenbewegungen und Beanspruchungen, wie sie für die Planung von Vortrieben insbesondere unter setzungsempfindlichen, innerstädtischen Gebieten erforderlich sind. Darüber hinaus stellt das Modell ein wertvolles Hilfsmittel bei der vortriebsbegleitenden Steuerung von Vortriebsmaschinen in Lockergestein dar. Neben den wesentlichen Komponenten des numerischen Modells, des Modellgenerators und der Dreiphasen-Formulierung für den Boden enthält der Beitrag als prototypisches Anwendungsbeispiel die Simulation einer Druckluftintervention in Lockergestein. [source] Mechanical Response of Single Plant Cells to Cell Poking: A Numerical Simulation ModelJOURNAL OF INTEGRATIVE PLANT BIOLOGY, Issue 6 2006Rong Wang Abstract Cell poking is an experimental technique that is widely used to study the mechanical properties of plant cells. A full understanding of the mechanical responses of plant cells to poking force is helpful for experimental work. The aim of this study was to numerically investigate the stress distribution of the cell wall, cell turgor, and deformation of plant cells in response to applied poking force. Furthermore, the locations damaged during poking were analyzed. The model simulates cell poking, with the cell treated as a spherical, homogeneous, isotropic elastic membrane, filled with incompressible, highly viscous liquid. Equilibrium equations for the contact region and the non-contact regions were determined by using membrane theory. The boundary conditions and continuity conditions for the solution of the problem were found. The force-deformation curve, turgor pressure and tension of the cell wall under cell poking conditions were obtained. The tension of the cell wall circumference was larger than that of the meridian. In general, maximal stress occurred at the equator around. When cell deformation increased to a certain level, the tension at the poker tip exceeded that of the equator. Breakage of the cell wall may start from the equator or the poker tip, depending on the deformation. A nonlinear model is suitable for estimating turgor, stress, and stiffness, and numerical simulation is a powerful method for determining plant cell mechanical properties. (Managing editor: Wei Wang) [source] Performance of a guideway seismic isolator with magnetic springs for precision machineryEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 2 2009George C. Yao Abstract This paper proposes the use of the nonlinear restoring force in an isolation system to improve the performance of a seismic isolator. Nonlinear magnetic springs applied to guideway sliding isolators (GSI) that protect precision machinery against seismic motion were studied. The magnetic springs use a non-contact magnetic repulsion force to achieve a nonlinear property. A numerical simulation model of the GSI system using step-by-step integration in the time domain was developed. A full-scale shaking table test was performed to verify the accuracy of the numerical model. Simulation and experimental results show that the GSI system with magnetic springs has good performance when subjected to floor vibrations during earthquakes. A parametric analysis of the magnetic springs in the GSI system under seismic motion was theoretically investigated. It was found that sufficient magnetic forces can diminish the system relative displacements. Copyright © 2008 John Wiley & Sons, Ltd. [source] Vents and seals in non-steady-state chambers used for measuring gas exchange between soil and the atmosphereEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 4 2001G. L. Hutchinson Summary Despite decades of research to define optimal chamber design and deployment protocol for measuring gas exchange between the Earth's surface and the atmosphere, controversy still surrounds the procedures for applying this method. Using a numerical simulation model we demonstrated that (i) all non-steady-state chambers should include a properly sized and properly located vent tube; (ii) even seemingly trivial leakiness of the seals between elements of a multiple-component chamber results in significant risk of measurement error; (iii) a leaking seal is a poor substitute for a properly designed vent tube, because the shorter path length through the seal supports much greater diffusive gas loss per unit of conductance to mass flow; (iv) the depth to which chamber walls must be inserted to minimize gas loss by lateral diffusion is smaller than is customary in fine-textured, wet or compact soil, but much larger than is customary in highly porous soils, and (v) repetitive sampling at the same location is not a major source of error when using non-steady-state chambers. Finally, we discuss problems associated with computing the flux of a gas from the non-linear increase in its concentration in the headspace of a non-steady-state chamber. [source] A Numerical Simulation Model for Shield Tunnelling with Compressed Air SupportGEOMECHANICS AND TUNNELLING, Issue 3 2008Felix Nagel Dipl.-Ing. This paper is concerned with a numerical simulation model (ekate) specifically designed for shield tunnelling in fully and partially saturated soils based upon the Finite Element Method (FEM). The model considers all relevant components , the soil, the lining, the tail void grouting, the hydraulic jacks and different types of face support , involved in shield tunnelling. The surrounding soft soil is formulated as a three-phase material, consisting of the soil skeleton, pore water and air. This model allows for the simulation of consolidation processes in partially saturated soils as well as of flow of compressed air often used as temporary face support during repair interventions at the cutting wheel. Despite the complexity connected with the relatively high degree of realism of the simulation model, only little effort is required from the user to establish a realistic 3D model for shield tunnelling. To this end an automatic model generator has been developed which allows for a user friendly generation of the discretized model including all components involved and to investigate variants with a minimum effort for the user. The model allows for realistic predictions of settlements and also provides information on deformations and stresses in the ground, the lining and the TBM, respectively. In addition to its use as a prognosis tool in the design process, in particular for tunnelling projects in sensitive urban areas, the model also may be used to assist the driving and steering process in mechanized tunnelling. The paper provides an overview over the main components of the model, the automatic model generator and the tri-phasic representation of the soil. A simulation of a compressed air intervention of a shield tunnel in soft soil demonstrates the applicability of the model. Ein numerisches Simulationsmodell für druckluftgestützte Schildvortriebe In diesem Beitrag wird ein Simulationsmodell basierend auf der Methode der Finiten Elemente (FEM) für die Berechnung schildvorgetriebener Tunnel in un-, voll- und teilgesättigten Böden vorgestellt. In diesem numerischen Modell werden alle beim maschinellen Tunnelbau wesentlichen Komponenten , der Boden, der Ausbau, die Schildschwanzverpressung, die Vortriebspressen sowie unterschiedliche Arten der Ortsbruststützung , wirklichkeitsnah berücksichtigt. Der Baugrund wird im Simulationsmodell als dreiphasiges Material modelliert, bestehend aus dem Korngerüst, dem Porenwasser und der Porenluft. Diese Materialformulierung für den Baugrund ermöglicht die Analyse von Konsolidierungsprozessen in teilgesättigten Böden ebenso wie von Strömungsvorgängen im Boden bei Verwendung von Druckluft als temporärer Ortsbruststützung. Druckluft wird häufig beim Wechsel von Schneidwerkzeugen eingesetzt. Ungeachtet der Komplexität des Modells, die mit der relativ wirklichkeitsnahen Abbildung des Vortriebsgeschehens verbunden ist, ist nur ein sehr geringer Aufwand für die Modellgenerierung erforderlich. Um diesen Eingabeaufwand auf ein Minimum zu reduzieren, wurde ein automatischer Modellgenerator entwickelt, der den Ingenieur bei der Eingabe unterstützt und die Untersuchung von Planungsalternativen deutlich vereinfacht. Das Modell ermöglicht wirklichkeitsnahe Prognosen von Bodenbewegungen und Beanspruchungen, wie sie für die Planung von Vortrieben insbesondere unter setzungsempfindlichen, innerstädtischen Gebieten erforderlich sind. Darüber hinaus stellt das Modell ein wertvolles Hilfsmittel bei der vortriebsbegleitenden Steuerung von Vortriebsmaschinen in Lockergestein dar. Neben den wesentlichen Komponenten des numerischen Modells, des Modellgenerators und der Dreiphasen-Formulierung für den Boden enthält der Beitrag als prototypisches Anwendungsbeispiel die Simulation einer Druckluftintervention in Lockergestein. [source] EXTERNALITIES AND PARTIAL TAX REFORM: DOES IT MAKE SENSE TO TAX ROAD FREIGHT (BUT NOT PASSENGER) TRANSPORT?,JOURNAL OF REGIONAL SCIENCE, Issue 4 2007Edward Calthrop ABSTRACT Externalities such as pollution and road congestion are jointly produced by the use of intermediate inputs by firms and the consumption of final goods by households. To cope with such externalities, policy proposals often suggest partial tax reforms. This paper uses a simple general equilibrium model to explore the effects of a reform of taxes on freight transport in a second-best setting. The theoretical model shows that the welfare effect of higher freight taxes is positive, unless passenger transport is severely under-taxed and the tax reform attracts substantially more passenger transport. Moreover, the optimal freight tax may be below or above marginal external cost. Budgetary neutral tax reform exercises with a numerical simulation model for the U.K. suggest that, under a wide variety of parameter values, higher freight transport taxes are indeed welfare increasing. The welfare gain of freight tax reform rises with the level of the passenger tax, but the optimal freight tax declines at higher taxes on passenger transport. Substantial net benefits of tax reform are obtained only under labor tax recycling of the revenues. [source] NUMERICAL MODELING AND SIMULATION ON THE SWALLOWING OF JELLYJOURNAL OF TEXTURE STUDIES, Issue 4 2009H. MIZUNUMA ABSTRACT Studies of the swallowing process are especially important for the development of care foods for dysphagia. However, the effectiveness of experiments on human subjects is somewhat limited due to instrument resolution, stress to the subjects and the risk of aspiration. These problems may be resolved if numerical simulation of swallowing can be used as an alternative investigative tool. On this basis, a numerical model is proposed to simulate the swallowing of a simple jelly bolus. The structure of the pharynx was modeled using a finite element method, and the swallowing movements were defined by pharynx posterior wall shift, laryngeal elevation and epiglottis retroflexion. The rheological characteristics of the jelly were investigated using an oscillatory rheometer and a compression test. A Maxwell three-element model was applied to the rheological model of the jelly. The model constants were obtained from compression tests because the mode of deformation and the stress level of the compression tests were similar to those of the swallowed jelly. The frictional relationship between the organs and the jelly was estimated experimentally from some frictional measurements between the jelly and a wet sloping surface. The results of the simulations for the soft and hard jellies showed different patterns of swallowing that depended on their hardness, and the soft jelly produced faster swallowing because of its flexibility. PRACTICAL APPLICATIONS The object of this study is to develop a numerical simulation model of swallowing. Numerical modeling is suitable for the quantitative analysis of the swallowing process and may also be expected to enable a systematic study of care foods that are safe and offer some degree of comfort to patients suffering from swallowing disorders. The computer simulation can be used for evaluation without dangerous risks to the patient. [source] | ||||||||||